This invention relates to conductive adhesive compositions for use within the semiconductor industry, particularly for attaching semiconductors dies to substrates.
Adhesive compositions, particularly conductive adhesives, are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses are the bonding of integrated circuit chips to lead frames or other substrates, and the bonding of circuit packages or assemblies to printed wire boards.
One format for presenting the conductive adhesive is a self-supporting film, which provides the exact amount of adhesive in the precise area necessary for die bonding. Film adhesives have the advantage of either not flowing, or flowing in a very limited way, only at the time of binding, and can be prepared so that they are relatively tack free to enable handling and repositioning. In one convention, the film adhesive is laminated to the backside of a semiconductor wafer before the wafer is diced into individual semiconductor circuits. Handling and positioning of the film onto the wafer typically takes place at or near room temperature, but the adhesive composition can be adjusted to provide a substantial lack of tack at higher temperatures. Following correct positioning, warming the adhesive to the lamination temperature will provide a suitable tackiness to adhere the adhesive to the wafer for subsequent dicing processes.
High thermal conductivity and electric conductivity are the required performance characteristics for conductive films. These properties are highly dependent on the level of conductive filler in the composition of the film. The conventional conductive filler for these compositions is silver or silver-plated copper. When the silver or silver-plated copper loading exceeds about 80 weight percent, the adhesion of the conductive adhesive film declines with increasing silver loading.
It would be an advantage to provide a conductive adhesive film with sufficient conductive filler to obtain the properties of thermal and electrical conductivity needed, without reducing the adhesive level of the film.